Lucretia mentions a True Rune that she experienced when she was a child. It said that the True Rune rages, exploding and burning her hometown and charred corpses everywhere.

This got to be Fire Bringer War and considering her ethnicity. But then she mentioned she is 3 years old..she was born in 418 which means it happens in 421, but that happens when Brass castle was built, the True Fire Rune explosion's won't happen until 425. Is this simply a mistake?

I don't remember perfectly, but does it ever say in Suikoden III that it as exactly 50 years prior to the game's events that the rune went out of control? So maybe it's "roughly 50 years". Or Lucretia does not remember clearly.

Also, there are always small discrepancies. Suikoden V heavily alludes to Morgan being shipped away and crippled because he was an undefeated gladiator champion,but he could not have been older than 14 which seems very unreasonable to me.